In for a Kopek, in for a Ruble: Replacing HVPS on Tetrode amp

[Naysayer]

My 4cx300 tubes are starved for plate current.
After years of working on this, I may as well do it right. I'm replacing the entire HVPS. Voltage Doubler replaced with a FWB driven by a different transformer rated for 1800v @ 400mA (Heathkit 54-30). No more combo trannies so I also ordered a 6v 10A open frame filament transformer with adjustable primary taps (110-115-120). It's been a while since I assembled W8JI's doubler board and I'm not certain if it can be reconfigured for FWB. If not, I need a sturdy FWB HVPS board too. Suggestion appreciated.

The plate windings on the Al-572 Ameritron transformer were repaired a decade ago after a short. The HV is not entirely symmetrical around the CT but still well over 2.2kv. I was disappointed by the plate current. It hovers around 100mA despite the 2.2kv key down voltage being stiff. Initial key down peaks are very high but it quickly falls down. Far from the 350-400mA I expected. The 16A filament windings are intact as are the Buck Boost windings so perhaps it can be salvaged as a filament transformer on a larger amp/tube that's too big for my future. Two 300a only require 6A plate current anyway so the transformer swap will lighten the overall weight. That's the plan, anyway. Ordered the transformers and looking for a HVPS board suitable for a FWB of 2.5kv at half an Amp.

The Titanic Submersible tragedy was a real Bummer to watch on TV last few days. Never realized RF does not travel in deep water.
Neil, NY City
PS: Error: end of 2nd para. "6A plate current" should read "6A filament current". Whoops!

 

[nomadradio]

I assembled W8JI's doubler board and I'm not certain if it can be reconfigured for FWB.

A full-wave doubler is one half of a full-wave bridge. You'll need to duplicate the rectifiers already in it to build a doubler into a bridge.

The board we sell for the Pride DX300 works either way. Taking a full-wave bridge and making a doubler out of it is no big trick. We're close to selling it configured as a doubler, to use a toroid HV transformer still on the market. The original HV transformer is no longer sold. The one we can buy has half the voltage of the stock tranny, but does the job for one tube that way. A package deal with the new toroid HV transformer and FW doubler HV board is still in the works.

I have a few of that board configured already to use as a doubler. The filter caps are 220uf, rather than the 100uf used with the bridge circuit. It would be listed to sell on fleabay if not for the instructions. Another of those "round tuits".

Adding the missing half of the rectifier diodes would make that one work as a bridge, like the stock config. The larger filter caps are probably wise for use with two tubes.

Let me know if you're interested. I'm sure we could work out a deal.

73

 

[Naysayer]

It's been a few years since I made a doubler from the 1st board. If it's the same board, I'll strip the board down and reinstall diodes & caps.

I attempted to find the board on your website but did not locate. Quality board thick plating that withstands re-soldering mistakes lol. CTR website?
Is it still posted online?

 

[Naysayer]

Found it. I see the Rectifier & Cap boards currently listed on CTR are separate.

EDIT: I got the HVPS board out today. I cannot justify not re-using it because it's just what I need and in great shape. I can also see that it's set for FWB if I add the remaining diodes. I had an extra 2 more caps (8 total) that obscured the additional cap markings on the boards.
I should get new and larger caps if I'm only using 6--I have the room height-wise if I can find the same diameter.
Thanks for a quality product Nomad.